There has been a continuing need for improved bone graft materials. Although autograft materials, the current gold standard for bone grafts, have the acceptable physical and biological properties and also exhibit appropriate structure, the use of autogenous bone also necessarily exposes the patient to multiple surgeries, considerable pain, increased risk, and morbidity at the donor site. Alternately, allograft devices may be used for bone grafts. Allograft devices are processed from donor bone and so also have appropriate structure with the added benefit of decreased risk and pain to the patient, but likewise incur the increased risk arising from the potential for disease transmission and rejection. Autograft and allograft devices are further restricted in terms of variations on shape and size and have sub-optimal strength properties that further degrade after implantation. Further, the quality of autograft and allograft devices is inherently variable, because such devices are made from harvested natural materials. Also, since companies that provide allograft implants obtain their supply from donor tissue banks, supply is uncontrolled since it is limited to the donor pool, which may wax and wane. Likewise, autograft supplies are also limited by how much bone may be safely extracted from the patient, and this amount may be severely limited in the case of the seriously ill and weak.
Since 2001, nearly 150 varieties of bone graft materials have been approved by the FDA for commercial use. Recently, synthetic materials have become an increasingly viable alternative to autograft and allograft devices. Synthetic graft materials have the advantages of not necessitating painful and inherently risky harvesting procedures on patients, have a minimal associated carry risk of disease transmission, and may be strictly quality controlled. Synthetic graft materials, like autograft and allograft, serve as osteoconductive scaffolds that promote the ingrowth of bone. As bone growth is promoted and increases, the graft material resorbs and is eventually replaced with new bone.
Many synthetic bone grafts include materials that closely mimic mammalian bone, such as compositions containing calcium phosphates. Exemplary calcium phosphate compositions contain type-B carbonated hydroxyapatite [Ca5(PO4)3x(CO3)x(OH)], which is the principal mineral phase found in the mammalian body. The ultimate composition, crystal size, morphology, and structure of the body portions formed from the hydroxyapatite are determined by variations in the protein and organic content. Calcium phosphate ceramics have been fabricated and implanted in mammals in various forms including, but not limited to, shaped bodies and cements. Different stoichiometric compositions, such as hydroxyapatite (HAp), tricalcium phosphate (TCP), tetracalcium phosphate (TTCP), and other calcium phosphate salts and minerals, have all been employed to match the adaptability, biocompatibility, structure, and strength of natural bone. The role of pore size and porosity in promoting revascularization, healing, and remodeling of bone has been recognized as an important variable for bone grafting materials.
Despite these recent advances, there is a continuing need for synthetic bone graft systems. Although calcium phosphate bone graft materials are widely accepted, they lack the strength, handling and flexibility necessary to be used in a wide array of clinical applications. Heretofore, calcium phosphate bone graft substitutes have been used in predominantly non-load bearing applications as simple bone void fillers and the like. For more clinically challenging applications that require the graft material to take on load, bone reconstruction systems that pair a bone graft material to traditional rigid fixation systems are used. For instance, a resorbable graft containment system has been developed to reinforce and maintain the relative position of weak bony tissue such as bone graft substitutes or bone fragments from comminuted fractures. The system is a resorbable graft containment system composed of various sized porous sheets and sleeves, non-porous sheets and sleeves, and associated fixation screws and tacks made from polylactic acid (PLA). However, the sheets are limited in that they can only be shaped for the body when heated.
In another example, one known bone graft substitute system incorporates flat, round, and oval shaped cylinders customized to fit the geometry of a patient's anatomical defect. This system is used for reinforcement of weak bony tissue and is made of commercially pure titanium mesh. Although this mesh may be load bearing, it is not made entirely of resorbable materials, leaving metal mesh residue in the body after the healing process has run its course.
Thus, there remains a need for resorbable bone grafts with improved handling, flexibility, and compression resistance. The present novel technology addresses this need.